Greenhouse gas emissions must peak in the next 10 to 15 years and then start going down if the world is to avoid the worst effects of global warming, scientists warned yesterday. Dr Bert Metz, co-chairman of the UN Intergovermental Panel on Climate Change (IPCC) working group, said emissions of carbon dioxide and other greenhouse gases could be reduced. Dr Robert Watson, overall chairman of the IPCC, said one option would be to store CO 2 in depleted oil wells - "putting the carbon back where it came from in the first place".
Dr Watson said it did not matter in the short term whether CO 2 emissions were reduced or stored. But he cautioned that using forests as carbon "sinks" was only a short-term measure.
He believed planting more trees would help reduce greenhouse gas concentrations. Dr Metz said the technology of pumping CO 2 into deep wells underneath the ocean was used in Norway, encouraged by carbon taxes to make it economically attractive.
"The basic idea is to capture CO 2 so that it doesn't get into the atmosphere," he said. Without such solutions and more conventional methods of combating climate change, he said, emissions could increase fivefold.
Dr Metz, the IPCC's leading specialist on mitigation measures, said improving energy efficiency, producing more fuel efficient vehicles and investing in solar and wind power would all help to reduce CO 2 emissions.
"If you add them all up and also include forests as carbon sinks, emissions can be brought down with currently available technologies," he said. "Implementing the Kyoto Protocol needs nothing new or fancy."
He stressed that the use of emissions trading - a mechanism being negotiated in Bonn - would keep costs down, in most cases below 1 per cent of GDP. This is below the level feared by the US. The impact on oil-producing countries would be greater, but would still be below 2 per cent of GDP - though there would be a "significant loss" in oil revenue. This was likely to be about 12 per cent on average.
In the long term, Dr Metz said, it was difficult to estimate the cost of making deeper cuts in emissions. But in most cases it would involve "doing the right thing" in investing in energy and transport.
The "real obstacles" to progress were economic or political. Fossil fuel prices were still too low by comparison with renewable energy and there were also "political barriers" to change.
Though it was a matter of judgment to assess the risks inherent in climate change or the levels at which greenhouse gases should be stabilised to avoid it, Dr Metz said "early mitigation action is imperative".
Dr Watson said there was "absolutely no doubt that the climate is warming", with simultaneous changes in rainfall patterns, a rise in sea levels and 60,000 non-polar glaciers starting to melt.
There was "no doubt" that most of this warming "is due to us" and, in particular, to the burning of fossil fuels. There was also "no doubt" that further climate change was "inevitable"; only its scale was at issue.
Even President Bush said this week global warming was a serious issue that should be addressed. "He did not say that action was not needed, only that he didn't see Kyoto as the way forward."
Asked about the variation in the IPCC's projected increase in temperature this century, from 1.4 degrees to 5.8 degrees, Dr Watson said it had ruled out the idea of producing a "probable" figure.
However, he agreed with a report published yesterday in Science magazine that it was likely to be in the mid-range of 3 degrees, taking into account population and economic growth.
Asked if the IPCC regarded CO 2-free nuclear power as having potential to combat climate change, Dr Watson said that while it could meet energy needs there were "other concerns" about its use, such as radioactive waste.
